The subject invention is directed toward the valve art and, more particularly, to an improved ball valve structure.
The invention is especially useful for forming large diameter ball valves for use in gas distribution systems and will be described with reference thereto; however, the invention is capable of broader application and could be used for valves of a variety of sizes in many environments and for different fluids.
Plastic pipe and compatible plastic valves have come into widespread use in gas distribution systems. These systems often require large diameter valves that are infrequently operated but which must be highly reliable. Several different plastic ball and plug type valve designs have been in use or proposed for use in such systems. These designs are shown, for example, in the following U.S. Pat. Nos. 4,047,275; 4,523,740; 4,540,157; 4,744,390; 4,794,944; 5,067,691; and, 5,076,542.
The various designs shown in these patents rely on relatively complicated, multi-component body designs or troublesome assembly procedures to achieve proper sealing engagement between the ball or plug and the associated seat rings. In addition, the designs frequently require that the body and valve element components be molded to very close tolerances. This necessitates the use of comparatively expensive dies or molds. Alternatively, it has sometimes been necessary to use separate locating elements to assure proper relative positioning of the body components.